The present invention provides novel hydroxyaromatic oligomers prepared from co-oligomerization reaction of a mixed cyanate of a polyphenol with an aromatic polyamine, as well as epoxy resin compositions prepared from said oligomers.
Preparation of hydroxyaromatic oligomers containing triazine groups and polyepoxides thereof is taught by R. E. Hefner, Jr., in U.S. Pat. No. 4,489,202 issued Dec. 18, 1984. The process disclosed therein uses an easily prepared mixed cyanate of a diphenol or polyphenol. More specifically, the process disclosed comprises reacting at least one material having an average of more than one aromatic hydroxyl group per molecule with at least 0.01 but not more than 0.95 moles of cyanogen halide or mixture of cyanogen halides per aromatic hydroxyl group at a temperature and time sufficient to essentially complete the reaction and thereafter recovering the resultant cyanate mixture; trimerizing the resultant cyanate mixture in the presence of a suitable trimerization catalyst at a temperature and time to essentially complete the reaction, epoxidizing the resultant trimerized product in a conventional manner by reaction with an epihalohydrin with subsequent dehydrohalogenation with a basic-acting material and finally recovering the resultant triazine functional glycidyl ether product. Excellent control over the molecular weight and content of triazine groups is provided by this process. The resultant epoxy resin compositions possess unusually high thermal stability as well as excellent overall physical and mechanical properties.
Preparation of hydroxyaromatic oligomers containing triazine and oxazoline groups and polyepoxides thereof is taught by R. E. Hefner, Jr., in U.S. Pat. No. 4,487,915 issued Dec. 11, 1984. The process disclosed therein uses the aforementioned mixed cyanate of a diphenol or polyphenol. Co-oligomerization of this cyanate mixture with an epoxy resin, such as a diglycidyl ether of bisphenol A, provides hydroxyaromatic oligomers containing both triazine and oxazoline groups. Oligomers prepared from co-oligomerization of the mixed cyanate of a diphenol with an epoxy resin using mole ratios of epoxy groups to cyanate groups of about 1 to 10 to about 1 to 40 or more are disclosed for the process described. The oligomers, and unreacted diphenol, if any, are then epoxidized using methods well known in the art. The resultant epoxy resin compositions possess excellent thermal stability as well as enhanced mechanical properties.
Preparation of advanced epoxy resin compositions containing triazine groups or both triazine and oxazoline groups are taught by R. E. Hefner, Jr., in allowed application Ser. No. 582,415 filed Feb. 22, 1984. In the process disclosed therein, the respective triazine-containing or triazine-containing and oxazoline-containing hydroxyaromatic oligomers are reacted with an epoxy resin. The application discloses advanced epoxy resins as well as cured compositions thereof.
The hydroxyaromatic oligomers of the present invention contain both triazine groups and ##STR1## linkages, otherwise called "imino carbamate". The oligomers are prepared by co-oligomerization of a mixed cyanate of a polyphenol with an aromatic polyamine in the process of the present invention. In the process, the polyphenol, such as 4,4'-isopropylidenediphenol (Bisphenol A) is reacted with less than a stoichiometric equivalent of a cyanogen halide in the presence of an alkaline agent, such as triethylamine. This provides a mixture of monocyanate, dicyanate and, optionally, unreacted diphenol. Co-oligomerization of this mixture with the desired amount of an aromatic polyamine, such as methylenedianiline, provides hydroxyaromatic oligomers containing both triazine groups and imino carbamate linkages. Epoxidation of the oligomers and unreacted diphenol, if any, using methods well known in the art provide the epoxy resin compositions of this invention. Advancement reaction of the oligomers and unreacted diphenol, if any, and an epoxy resin using methods well known in the art provide advanced epoxy resin compositions of this invention.
Although included within the scope of this invention, oligomers prepared from co-oligomerization of the mixed cyanate of a diphenol with an aromatic diamine wherein the mole ratio of amine groups to cyanate groups is less than about 1 to 5, respectively, are generally either reactive with or insoluble in the solvent(s) and/or reactant(s) useful in epoxidation reactions but are useful as thermoset resins. Oligomers prepared from co-oligomerization of the mixed cyanate of a diphenol with an aromatic diamine wherein the mole ratios of amine groups to cyanate groups are about 1 to 5 to about 1 to 40 are most preferred precursors to the epoxy resins of the present invention.
Unreacted diphenol (polyphenol), which is preferably present as a component of the oligomers, is converted to the corresponding diglycidyl ether during the epoxidation of the hydroxyaromatic oligomers. This improves overall processability of the epoxy resin. If desired, extra diphenol can be added prior to epoxidation to increase the diphenol diglycidyl ether content of the finished epoxy resin product. Likewise, extra dicyanate may be added to the cyanate mixture prior to co-oligomerization.